Hemiepiphysiodesis systems are used for the correction, arresting or slowing of abnormal curvature of the spine, including scoliosis, hyperlordosis and hypokyphosis. Such spinal correction systems bridge vertebra that remain active. However, since the vertebral bodies are still in motion, a gradual dislodgment or outward movement of the fastener could result. As with vertebral plates, partial protrusion of one or more fasteners could damage surrounding structures such as the lung (or the esophagus for cervical plate) and, in a worst case scenario, could permit the plate or correction system to dislodge.
Vertebral (e.g. cervical) plates and other spinal correction systems using hemiepiphysiodesis principles and fastener retention are known in the art. U.S. Pat. No. 6,746,450 to Wall et al., for example, discloses a system that includes a bridge member, a pair of spaced apart barbed legs extending substantially perpendicularly therefrom, and a fastener retaining portion extending substantially longitudinally from each end of the bridge member. The fastener retaining portions are adapted to lie in adjoining relationship when two or more spinal correction systems are arranged in end-to-end abutting relationship. The spinal correction system is intended to correct or arrest scoliosis in a growing spine by spanning the endplate growth centers of adjacent vertebrae, on the convex side of the malformed spine, to retard growth of that side of the spine while permitting unrestrained growth of the concave side of the spine.
Other Fastener Retention features are disclosed in U.S. Pat. No. to 4,794,916 Wolter, which teaches a plate to cover the fastener head to prevent back out. Other patents and applications that cover the fastener head to retain the fastener include U.S. Pat. No. 6,602,255 to Campbell; U.S. Pat. No. 6,599,290 to Bailey; U.S. Pat. Nos. 6,527,776, 6,193,721, 6,139,550 and 2005/059971 to Michelson; U.S. Pat. No. 6,235,034 to Bray; U.S. Pat. No. 5,954,722 to Bono; U.S. Pat. Nos. 5,876,402, 5,531,746 Errico et al. and U.S. Pat. No. 5,607,426 to Ralph et al. All use some type of cover, cap or set screw to cover or affix the fastener by totally or partially covering the screw head. U.S. Pat. No. 5,578,034 uses a snap-ring collar that captures the screw as it passes through it. The collar is made of a shape memory material that locks after placement. U.S. Pat. Nos. 6,656,181 and 6,695,845 to Dixion et al. uses a tapered pin that yields the plate such that frictional force holds the screw and pin together. U.S. Pat. No. 6,695,846 and published application Nos. 2003/0187440, 2003/0187442, 2003/0187440, and 2004/0097935 to Richelsoph et al. disclose a snap-ring-like collar or movable collar that retains the fastener.
It is desirable to install vertebral plates and spinal corrective systems (implants), including the fasteners, endoscopicly. However, endoscopic installation requires good visibility, accurate placement and, perhaps most importantly, no additional steps or components associated with installation. For example, actuation of a fastener retention system as a separate step after installation of the fastener is not desirable. Such added steps consume valuable and expensive time, requiring the patient to remain under general anesthesia longer adding to the procedural risk. Accordingly, a simple and easy to install fastener retention system and method is needed to reduce the complexity and cost of spinal correction.